The Efficiency and Relevance of Different Concentration Methods for the Analysis of Off-Flavours in Water

The efficiency of four different concentration methods (stripping with and without addition of salt, XAD-2 adsorption and dichloromethane extraction) for the enrichment of off-flavour compounds in treated and untreated surface water has been evaluated by gas Chromatographic sniffing and by sensory analysis of the concentrated extracts. In general, the extracts obtained by dichloromethane extraction and XAD-2 adsorption contained a larger number of off-flavour compounds than the stripping extracts. Experiments in which the extracts from stripping and dichloromethane extraction were dissolved in odourless water showed that the original odour quality of the water could normally be re-created by both methods. However, for certain surface water samples, the original odour may be re-created from extracts obtained by solvent extraction but not from corresponding stripping extracts, proving that the choice of concentration method can be important. Fractionation of extracts by preparative gas chromatography followed by dissolving of the resulting fractions in odourless water, was found to be a powerful technique for isolating the organic compounds causing the off-flavour of a water sample.